Keepers have shot dead a chimp who escaped from his enclosure at Whipsnade Zoo in Bedfordshire.
The zoo was closed as staff tried to round up two chimps - called Jonnie and Coco - who escaped at about 1000 BST.
Visitors already in the park were told to stay in their cars or were taken to secure locations.
Coco was recovered unharmed, but keepers were unable to capture Jonnie safely and he was shot, said a Whipsnade Zoo spokesman.
An inquiry to find out how the pair, who were two of eight chimps at Whipsnade, got out of their three-year-old purpose built enclosure has started.
In a statement the zoo said: "As soon as members of staff were aware of the occurrence, the Escaped Animal Procedure was immediately commenced.
"All members of the public were led to safe and secure locations or instructed to remain in their vehicles."
The statement said there were no injuries to either staff or members of the public.
It added: "Keepers moved quickly to recapture the two chimpanzees, Jonnie and Coco.
"Procedures were followed by staff and in the interests of public safety, Jonnie was shot.
"Coco was quickly recaptured and is now safely in the hands of her keepers."
There were eight chimps at Whipsnade: 23-year-old Nicky, a male; Bonnie Louise who is 21; Zephyr, a 15-year-old male; Grant and Phil, both aged 11; Elvis, aged five, and Coco and Jonnie who were transferred from London Zoo in 2006.